Automatic switch



I Filed June 3, 1947 Jan. 8, 1952 o. A. PEARCE ET AL AUTOMATIC SWITCH 2 SHEETS-SHEET 1 FIG. I

INVENTORS. OWEN AVIS PEARCE Y REGINALD TAYLOR B K A ATTORNEY Jan. 8, 1952 o. A. PEARCE ET AL AUTOMATIC SWITCH 2 T E E H J S m x E HF u s 2 0 000 0 B l D o o 4 H A H 7 4 9 1 5 e n H J Q 6 l 1 F FIG. 2

INVENTORS. OWEN AVIS PEARCE By REGINALD TAYLOR ATTORNEY Patented Jan. 8, 1952 AUTOMATIC SWITCH Owen Avis Pearce and Reginald Taylor, Liverpool, England, assignors to Automatic Telephone & Electric Company Limited, Liverpool, England, a British Company Application June 3, 1947, Serial No. 752,213 In Great Britain June 19, 1946 9 Claims. I 1

'-'I he present invention relates to automatic switches of the type employed in telephone and like systems and is more particularly concerned with automatic switches which perform a group selecting function by testing for an'idle outlet to succeeding equipment marked by the presence of a particular potential upon the test conductor.

In previous switches the possibility has existed that an outlet tests busy but, while the wipers are stepping from that outlet to the next but before the wipers are clear of the outlet, the outlet becomes idle, whereupon the switching relay may have time to operate to that idle condition and cause the switchto seize the succeeding outlet irrespective of its idle or busy condition.

It is the main object of the present invention to provide arrangements which will reduce this possibility and according to the invention the stepping of the wipers from one outlet to the nextand the testing of the outlets is arranged to be effected sequentially without overlap. This ensures that no test circuit is available during the stepping of the switch and hence the possibility of the switching relay operating during stepping is substantially non-existent.

Preferably sequential stepping and testing is efiected by employing changeover rotary magnet interrupter contacts and arranging the circuits so that the rotary magnet is operated over the back interrupter contacts while the test circuit is completed over the front contacts. The switching relay can thus only operate when the wipers have completed the step and the rotary interrupter contacts are operated and the desired sequence of step; test; step; test is obtained.

7 The invention is also concerned with arrangements for releasing the equipment which precedes the group selecting switch particularly when the switch is of the battery testing type. It is usual practise in circuit design to arrange for a brief unguard period to occur before the release of a switch in order to initiate the release of the preceding switches in the train. On earth-testing'selectors it is easy to arrange for the unguard feature but on battery-testing selectors, which include a fast switching relay, the problem is more difflcult. It is a further object of the present invention-to avoid this difilculty and according to feature of the invention, a slow and a.

fast relay are operated in series to control the connectionto an idle outlet and on the release of the connection the circuit to said relays is opened, and'earth potential is removed from the private wire on the release of the fast relay and replaced on the release of the slow relay to provide the guarding earth is effected on the release of the switching relay under the control of oil-normal contacts. The initiation of the release may, of course, be due to the normal release of a con nection or it may be due to a fuse blowing in a succeeding switch.

It is well known that there are at least two methods in general use for the testing of switch outlets. In one of these busy lines are marked by earth potential while in the second idle lines are marked by battery potential. A further object of the invention is to enable the group selecting switch to operate with preceding equipment employing either method and this is effected'by means of a simple strapping between two tags, the existence of "the strapping'enabling the switch to operate with equipmentof one type and the absence enabling it to operate with equipment of the other type. i

The invention will be better understood from the following description taken in conjunction with Figs. 1 and 2 which show its application-to a switch of the so-called rectangular movement type as described in United States Patent No. 2,028,689 issued January 21, 1936 to R. N. Saxby having two sets of wipers and adapted to test two groups of outlets simultaneously.

The condition of the P conductor when the switch is in the normal position is determined by the requirements of the preceding equipment. Where this is of the battery testing type leads II and 2 are strapped to connect battery via resistor YA to the P conductor, whereas if the preceding equipment is of the earth testing type this strap is omitted to open the P conductor.

When the switch is taken into use relay A is operated over the loop by way of its outer windings, and thereupon completes a circuit from earth at contacts N2 to operate relay B in series with resistor YC and. vertical magnet VM. Re

lay B only operates over this circuit and at contacts Bl completes a locking circuit for itself, at

contacts B3 earths the incoming P conductor to hold the preceding switches, at contacts B2 completes a circuit to operate relay HA from battery' It may be mentioned here that the switch is equally suitable for use as a firstgroup selector,- an incoming selector or a subsequent groupse lector. If it is used as a first selector, the middlewinding relay A is, on the closure of contacts B5,

connected by way of cam contacts S2 and common lead l3 to dial tone, and the relay in known manner serves as a tone transformer so that dial tone is audible to the calling subscriber. If the switch is usedin positions other than the first selecting stage, dial tone is not connected to lead [3. Further, if the switch is used as a first selector, leads !9 and II may be strapped so that an immediate guard to the P conductor is provided by contacts Al over contacts N3 and HA! and test link TL2 in the manner described in United States Patent No. 2,424,519- issued July. 22, 1947 to Reginald Taylor :et a1.

Relay HA upon operating, at contacts HA! lays HX and HY simultaneously test the PI and short circuits resistor YC to prepare forvertical stepping, at contacts HA2 andHA6".prepares for the disconnection of relay A, at contacts HA3 opens a point in the RM rotary magnet drive circuit and completes a circuit in series with the rotary-magnet to .the common conductor :16 to light the individual supervisory lamp LP. The

common conductor 16 extends to exchange alarm equipment which provides a signal if the switch is seized but notoperated within a predetermined time.

No further changes take place until aseries of impulses forming a digitxis transmitted to the switch, whereupon relay A responds accordingly, and :on each 'de-energisation completes .a circuitifor magnet VM whichnow operates to raise the wipers a corresponding number'of steps. Relay B is short-circuited each time relay .A releases and consequently remains operated during the impulse train. As soon as the :switch moves off-normal the vertical off-normal contacts are'operated'and at contacts .Nl a point is closed in the rotary magnet drive circuit; 311300119,

tacts N2 the original operating earthfor relay B is removed and relay B is now dependent on its own contacts Bl- Contacts .3! also extend earth each time relay A operates, to short.cir-

cuit relay HA which, .howeveiysis slow-to-release and remains operated. Finally at contacts N3 a point is opened in the immediate guard -cir cuit, where this facility has. been used, and prepares the, release guard circuit.

At the end of the impulse train relay A remains steadily operated and relay HA is therefore short-circuited and releases, after a delay, 'to

complete the rotary magnet circuit f-romearth on common lead [5. The magnet therefore floperates to advance the switch wipers-into engagement with the-first set of bank contacts and, towards the end of the stroke, operates the interrupter contacts RMC which 'de-energise the magnet and completezPl and .P2 wiper testing circuits via the 'low resistance right-hand wind ings of .relays HX and HY respectively: :On the first rotary step the rotary ofi normal contacts NR operate and'at contacts NRI and NR4 make the subsequent disconnection of relay A dependentupon the operation of either the HAor HB switching relay; at contacts NR2 prevent false operation of the vertical magnet; at contacts NRa-ensures that resistor YC remains included in the vertical magnet circuit and at contacts NR5 connects the resistor YB across the rotary magnet. y

vFour possibilities now arise, viz..that wiper Pl will encounter an idle lineand wiper P2 a busy line, that both wipers will encounter idle .lines, that wiper P2 will encounter an idle line and counter busy lines.

wiper Pl a busy line, or that'both wipers will en-v P 2 bank contacts respectively, but relay HX aloneoperates from earth at common lead l5 extended by the operated RMC contacts via rectifier MRA, relay .HX right hand low resistance winding to .the battery potential on the Pl bank contact. :Contacts HXI opens a point in the rotary magnet circuit, to prevent further advancement of the wipers, and provide a circuit to energise relay HA and the left hand winding of relay HX in series with the rotary magnet, whereby relay HA is operated and'relay HX is locked. Contacts HXZ apply an immediate guard to the Pl bank contact, to cover the operate time of relay HA, thereby seizing the free OGA out let. Relay HA in operating, at contacts HA2 and HA4 connects the incoming (IC) negativeand positive speech wires to the OGA-outlet -l :and wipers, disconnects relay .A which releases and at contacts HA5 extends the P conductor to thePl wiper. Relay A releasing, at contacts A! short circuitsrelay B which then releases slowly to remove the local guarding earth from the P conductor at contacts .33 and B4. Relays HA and HX now remain operated from earth returned over the P wiper.

If both outlets OClA and 0GB are idle, battery potentials are encountered by the .PI and P2 wipers, and the HX and HYrelays consequently operated. Contacts HX I prevent the operation of relay HB, and opena point-in the rotary 2magnet circuit and cause relay HA to operate as'in the case 'just described. The immediate guard applied at contacts HY2 to the P2 conductor is disconnected .at contacts HA8 and relay HY is released at the same contacts. Relay HA in "op-' erating causes relays A and B to release in turn;

In the third case in which the OGAoutlet is busy and the 0GB outlet is "idle, the P2 w-ip'er encounters a battery potential .and relay HY- operates from earth at lead I5-extended by op erated RMC contacts via rectifier MRB, relayHY low resistance right hand winding, contacts B5 and HA8 to the battery potential on wiper P2;

Contacts HYI open a point in the rotary magnet circuitand provide a circuit for energising relay HB andthe left hand winding of relay HY in series with the rotary magnetwhereby relay is operated and relay HY is locked. -Contacts HY2 apply an immediate guard to the P2 wiper; The speech conductors are extended to the 0GB outlet over operated contacts HBZ and HBB, .re--

In the fourth case in whichboth P! and wipers encounter busy outlets, relays HX and HY remain in operative and consequently, when the interrupter contactsRMC restore to normal;

, the rotary magnet is re-energised and advances "the: wipers'a further'step to the next set of bank contacts-where all four possibilities are again operative. It may be pointed out the speed of rotary stepping is controlled by the value of the shunt resistor YB. i

If the wipers are advanced over the .whole group without either wiper encountering a free outlet, they. attain the 1 Ith step position at which relay HY operates, from battery at resistor YA extended over contacts HBE, P2, Hth step bank contacts, contacts HA8 and B5, right hand windingof relay HY, rectifier MRB and contacts RMC to earth at lead l5. Relay HY in operating disconnects M'tofthef left hand and middle windings of relay A', andat contacts S2 busy tone earth from common leadv H is applied to the middle winding of relay Av- This relay again acts as a tone transformer by repeating the busy tone to the calling subscriber, and it remains operated on the middle winding during the battery period on lead 14.

It may be pointed out at this stage that the circuit arrangement obtains switching to busy outlets by ensuring that the PI and P2 testing circuits are applied whilst the interrupter contacts RMC are operated, and. the

rotary magnet RM is energised over contacts RMC normal, provided a test relay HX or HY is not operated, so that simultaneous closure of the other known battery testing switches.

It may be further pointed out that the circuit arrangement also obtains immunity from multiple connections in the case of two or more selcctors testing the same outlet simultaneously, by

of all switches concerned consequently continue to be advanced over the contacts until the faster switch is able to seize an outlet.

Upon the release of the connection at the end of the conversation, relays HA and HX or HB and HY, as the case may be, are disconnected :-rel'ease of the connection and again the P conlease time of relay HA or HB to release the pre= duotor holding earth is disconnected for the ref ceding equipment.

When the calling party hangs up in response to the receipt of busy tone, relay A releases during one of the earth periods on lead I l, and

, thereupon short circuits relay B. This relayzon "releasing removes earth from the P conductor at contacts'B3= and relays HA andHX or HBand "HY are-thereby released to function as in-the case of release on termination of a conversation.

We claim: 1. In a telephone system, an automatic switch,

'1 a first circuit including a magnet for. operating alternate battery and earth is extended" from common lead f said switch, a second circuit including a relay for stopping said switch, contacts on said magnet for controlling said first circuit, other contacts on said magnet for controlling said second circuit, saidcontacts being arranged so that saidfirst;cir-

cuit is closed only when said second circuit is ppm and saidsecond circuit is closed only when said first circuit is open.

2. In a telephone system, an automatic switch,

. incoming and outgoing conductors for said switch,

immunity from a plurality of contacts accessible to said outgoing conductors, a magnet for operating said switch -to thereby bring said outgoing conductors into engagement with individual ones of said contacts,

a relay for controlling the connection of said incoming conductors to contacts with which said 40" stepping and testing circuits does not occur as in outgoing conductors are engaged, a circuit for operating said relay, means for operatin said magnet, and contacts on said magnet for completing arranging that two or more testing relays, HX or HY, will not operate to a common battery po- .1

tential on a P! or P2 bank contact. The wipers the idle or busy condition thereof, and contacts said circuit only when said magnet is operated. 3. In a telephone system, an automatic switch adapted to hunt for an idle outlet in a group of outlets, means for moving said switch from one outlet to the next outlet, a, circuit for testing each outlet to which the switch is moved to determine in said switch for closing said circuit, said contacts arranged to prevent the closure of said circult during the movement of said switch from a contact with which it is associated.

4. A telephone system as set forth in claim 8 in which said circuit for testing each outlet in- V cludes a rectifier to prevent the operation of said ,circuit from a potential of one polarity which 'may be encountered on said outlets.

P conductor is maintained open to disconnect L the connection of said switch to an idle one of said lines, a control conductor to which guarding potential is at times connected, a holding circuit preceding equipment and after its release earth is re-applied by contacts HA1 or HB3 normal. Also when relay HA or HB releases the self-interrupted drive circuit to the rotary magnet is completed, from earth on lead l5 which extends to the alarm equipment, consequently the wipers are rotated clear of the banks and then returned to their home position where the off-normal contacts N restore. In restoring to normal contacts N3 remove earth from the P lead, and if necting guarding potential to said control conthe switch is preceded by other battery testing switches as evidenced by a strap connecting leads H and [2, apply battery via resistor YA to the P conductor.

I 5. In a telephone system, an automatic switch, 'a plurality of lines accessible to said switch, a fast relay and a slow relay operated to control for said fast relay and said slow relay from guardmentary disconnection of guarding Potential 0m said control conductor to disable said holdin cirductor to prevent seizure of said switch while it is releasing.

6. A telephone system as set forth in claim 5 '2 inf-which said automatic switch is arranged to hunt for an idle line in a group of lines, .said fast relay being effective for controlling the hunting operation of said switch and said slow relay being effective for completing the connection between said switch and an idle one of said lines.

7. In a telephone system, an automatic switch,

'a' fast to release relay, a slow to release relay, a control conductor to which guardin potential is at times connected, means for operating said switch, means 'for releasing said switch, means for operating the relays in case said switch "is operated, means for completing a holding circuit for the relays from guarding potential connected to said control conductor, said fast to release relay being efiective to release and disable said 8. In a'switching device, :a wiperset, a plurality of contact sets, first electro-mechanical means for moving said wiper set over said contact sets,

second electro-mechanical means for stopping said wiper set on one of said contact sets, a first "circuit for operating said first :electro-mechanical means, avsecond circuit including a wiper of said .wiper :set for operating" said second electro-mechanical means, contacts on said first electromechanical means, and means including said con-.- tacts for preventing the simultaneous closure of saidfirst circuit and said second circuit.

9. In an automatic switch, 'a plurality of stationary contacts, a, movable contact for engagement with said stationary contacts, a magnet. means for energizing said magnet to move said movable contact over said stationary contacts, a relay, a circuit including said movable contact forenergizing said relay to stop said movable con-- tact on one of said stationary contacts, and :means for preventing the simultaneous energization of said magnet and said relay. 7 V OWEN AVIS PEARCE.

REGINALD TAYLOR.

REFERENCES CITED The following references are 01' record in the file of this patent:

UNITED STATES PATENTS 

